1. Field of the Invention
This invention relates to a method and apparatus for image processing, and more particularly to a method and apparatus for image processing that extracts characteristics of an image and generates an image signal having multiple scale values in accordance with the extracted characteristics.
2. Discussion of the Background
In general, an image processing apparatus in use for various image handling apparatuses, such as a digital copying machine, a facsimile machine, and so forth, has been provided with a data handling operation that separates an original image having a mixture of characters and patterns into a plurality of image areas in accordance with types of images as determined with detailed analysis of the original image. This background apparatus then switches to an appropriate image processing operation according to the image type to appropriately process each separated image area. For example, Japanese Laid-Open Patent Publication No. JPAP03-089677 (1991) describes a technique for emphasizing a contrast of characters in black, in particular, by switching a spatial filter, a gamma conversion, a screening, and so forth, to process each image area of a non-character (non-active) edge, a colored-character edge, an intermediate-chroma character edge, or a black character edge. As another example, Japanese Laid-Open Patent Publication Nos. JPAP07-108019 and JPAP06-018439 (1994) describe a technique that generates a specific signal having multiple scale values for representing an edge of a character, as illustrated in FIG. 8. FIG. 8 illustrates a relationship between density scales of an edge and an immediately adjacent background, wherein the letter A indicates an edge of a character and the letter X indicates an area of an immediately adjacent background which can be analyzed relative to the edge A. Accordingly, this technique switches an image processing operation at multiple levels in accordance with the multiple scale values of the generated specific signal.
However, the technique of JPAP03-089677 has a drawback that a quality of an image deteriorates when the image has a sharply changed texture or when an erroneous image separation is made. This deterioration of image quality is due to a method of image separation using only binary scale values of 0 and 1 which may be insufficient to judge each image area. Also, the techniques of JPAP07-108019 and JPAP06-018439 have drawbacks that factitious marks remain around edges in the image caused by switching of the image processing operations, although the switching is conducted at the multiple levels and deterioration of an image is therefore decreased to a certain extent. As illustrated in FIG. 8, the reason for this drawback is that since this technique can use a 5-by-5 pixel filter at best, an area X of an immediately adjacent background which can be analyzed relative to the edge is relatively narrow.